Which metal is protected by a layer of its own oxide?

$A$. What are silicones? State the uses of silicones.
$B$. What are boranes? Give chemical equation for the preparation of diborane.

Which of the following reactions can be used to prepare diborane?
$I. BF_3 + LiAlH_4 \xrightarrow{\text{ether}}$
$II. BF_3 + NaH \xrightarrow{450 \ K}$
$III. Na_2B_4O_7 + H_2O \longrightarrow$
$IV. NaBH_4 + I_2 \longrightarrow$

Consider the following reactions.
$Na_{2}B_{4}O_{7} \xrightarrow{\Delta} 2 X + Y$
$CuSO_{4} + Y \xrightarrow{\text{Non-Luminous flame}} Z + SO_{3}$
$2Z + 2X + \text{Carbon} \xrightarrow{\text{Luminous flame}} 2Q + Na_{2}B_{4}O_{7} + CO$
The oxidation states of $Cu$ in $Z$ and $Q$, respectively are:

Boron trifluoride on reaction with lithium aluminium hydride in ether gives $LiF$, $AlF_3$ and $X$. $X$ on reaction with $NH_3$ gives $Y$. $Y$ on further heating gives a compound $Z$. The number of $\sigma$-bonds and $\pi$-bonds in $Z$ are $x$ and $y$ respectively. $(x+y)$ is equal to

$Na_2B_4O_7$ $\xrightarrow{x} H_3BO_3$ $\xrightarrow{\Delta} B_2O_3$ $\xrightarrow{y} B$
Here $X$ and $Y$ are respectively: